Quite common among digital front ends (DFEs) is the ability to identify object types (text, image, strokes, fill, line art, etc.) embedded in a given page description language (PDL) master. This is performed in the interpreter stage, prior to the actual imaging of the objects. These object types can then be used to optimize the processing of the contone data prior to transmission to the print engine. Several print engines now have the capability to accept “tags” or “hints” (in addition to the contone data) to optimize rendering, and these are generally assigned based solely on the object type. These tags or hints are generally specified for the entire object. For other engines, it is possible to supply rendering “hints” or “tags” for each pixel, allowing the engine to optimally render the objects on the page, pixel by pixel.
For example, in a print engine which specifies hints based on objects, all stroke objects might receive the “Stroke” hint, which might instruct the engine to render these objects with the system (e.g., a mid-frequency) halftone. This type of rendering may work well in situations where line art is intersecting a tinted fill background that is rendered with the same screen, avoiding potential screen switching artifacts. However, using the system halftone may not optimize colored text/line art sharpness in the case where these objects exist in isolation on a white background, as edges may appear excessively ragged. Instead, it may be desirable to render these with a higher frequency halftone screen, or even to enable additional edge enhancements (such as outlining). In this sense, there is a need to identify certain objects that exist solely on white background in order to prevent screen switching artifacts and to provide optimized rendering for such objects.